1. Field of the Invention
The present invention relates to an automatic electronic flash device (hereinafter called merely "strobo") for use in a flash photography system which automatically determines a diaphragm aperture by the aid of a preliminary flash light produced prior to production of a primary flash light with the intensity of preliminary flash light maintained substantially constant, and more particularly it pertains to a control device of the strobo for controlling a preliminary flash and a primary flash in accordance with signals from a camera.
2. Description of Prior Arts
In known automatic diaphragm control cameras which perform T.T.L (through the lens) light measurement through the diaphragm aperture being stopped down and which includes means to arrest the diaphragm when the value of the light measurement represents a given relationship with respect to a reference level, the diaphragm aperture is determined to its fully open aperture for such a low scene brightness condition that requires a flash illumination although it is desirable to set the diaphragm aperture to a specific size such as F5.6 for flash photography.
A flash photography system which eliminates this drawback has been proposed in Co-pending patent application Ser. No. 207,026 filed on Nov. 14, 1980, titled "CAMERA DIAPHRAGM CONTROL DEVICE FOR FLASH PHOTOGRAPHY" and assigned to the same assignee. The proposed system employs a strobo which produces a preliminary flash light prior to production of a primary flash light with the intensity of the preliminary flash light maintained substantially constant at least for the period required for the diaphragm to be stopped down to a specific aperture. As the scene to be photographed is illuminated by the preliminary flash light, the diaphragm is allowed to be stopped down and a diaphragm arresting means arrests the diaphragm thus being stopped down when the value of the T.T.L light measurement represents a given relationship with respect to a reference signal which has been stored prior to initiation of the diaphragm stop down operation in accordance with information of the desired specific aperture and the value of the T.T.L light measurement through the fully open diaphragm aperture. For these operations of the proposed system, signals are to be transmitted from a camera to a strobo at least for the control of the preliminary flash and the control of the primary flash and thus the number of the signal transmission contacts or terminals is increased on the strobo as well as on the camera. However, an increase of the number of signal transmission contacts or terminals generally leads to an increase in occurrence of troubles due to fault in conduction or misconduction between the corresponding contacts caused by corrosion of those contacts and the like.